Plastic resin is generally a high molecular weight polymeric material with no definite boiling point, but which is capable of flowing under heat and presssure, if necessary, into a desired final shape. Plastic articles are commonly produced from pellets formed of material comprising various blends of plastic resins and additives, wherein the resin pellets are extruded or molded to make the plastic article. In the production of plastic articles such as films, containers, etc., an important property of the article is the number and size of flaws that occur over a unit area of the article. One type of flaw that commonly occurs in plastic material is that of gels or fish eyes. As used herein gels and fish eyes are synonymous terms referring to a particle in a plastic material which differs from the surrounding resin to such a degree that it is not dispersed in the surrounding resin. Gels are readily discernable in thin plastic material.
In present processes for production of plastic pellets which typically contain gels, there is virtually no on-line method to detect flaws such as gels in the pellets as the pellets are being produced. Existing methods typically involve obtaining a sample of the pellets from a finished pellet transporting system as they are being produced, and performing a quality control test in a laboratory to determine if the pellets meet preestablished specifications. If the quality control sample fails to meet the specification standard, large quantities of product made while the control sample was being analyzed may have to be downgraded or reprocessed. This obviously is expensive.
It is therefore an object of this invention to provide method and apparatus for detecting, on line, flaws such as gels in the pellets so as to enhance quality control of the pellets by reducing the mixing of pellets having a low gel count with those having a high gel count.